Recovery of Metals from Electroplating Waste Solutions and Sludge. Comparison of Donnan Dialysis and Pertraction Technique
R. Wodzki1, P. Szczepanski1, M. Pawlowski2
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1Faculty of Chemistry, Nicolaus Copernicus University, Toruń, Poland
2Apator SA, Toruń, Poland
Pol. J. Environ. Stud. 1999;8(2):111-124
An experimental study has been made on the recovery, separation and concentration of some metals from electroplating solutions and sludge. Two membrane methods, i.e., the Donnan dialysis (DD) and the pertraction in a multimembrane hybrid system (MHS) were used and compared. Related ionic fluxes and separation coefficients for uni- and divalent cations were measured and discussed. It was found that the DD as a simple membrane technique can be used to permeate Zn2+ and Cu2+ with high fluxes associated with fluxes of other cations (Na+, Ca2+, Mg2+). The selective recovery of Zn2+ at the presence of Mg2+, K+, and Na+ was reached in the MHS composed of cation-exchange membranes and a liquid membrane containing di-(2-ethylhexyl) phosphoric acid (D2EHPA) or bis(2,4,4-trimethylpentyl) thiophosphinic acid (Cyanex 302) as a selective carrier. In the case of solutions remaining after zinc electroplating, the Zn2+ flux was 1.6x10-11 mol/cm2s, and separation coefficients aZnS gained the value of 8-10. The use of the MHS for processing dissolved and acidified sludge (pH~1) allowed to recover Zn2+ with the transport stationary rate equal to 3.2x10-11 mol/cm2s. According to the D2EHPA properties, other cations as Cr3+, Fe3+, Cu2+, Mg2+, and Na+ have not been transported to the stripping solution (1 M H2SO4). The use of Cyanex 302 instead of D2EHPA considerably lowers the flux of calcium and leads to the effective separation Zn2+ over Ca2+.
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